Vehicles such as a hybrid vehicle and an electric automobile are mounted with a large-capacity secondary battery for driving a motor. In the secondary battery, because the electric characteristic is reduced under a low-temperature environment, the capacity which can be charged and discharged is substantially reduced. In particular, because the electrolyte solution in a lithium ion secondary battery has high viscosity, internal resistance is increased under a low-temperature environment, and sufficient performance cannot be achieved.
In consideration of the above, in order to improve the battery characteristic under low-temperature environments, a system for warming the secondary battery is proposed (in, for example, JP 2008-290636 A and JP 2008-230508 A).